Electrolytic production of titanium tetrahalides



United States Patent Ofiice Bfiidlifidd Fatented Aug. 31, 165

3,263,889 ELECTRQLYTTQ PRCDUQTKUN F TlTi ai liilh'i TETEAHALEDES Robert William Ancrum, Paris, France, and Arthur Wat-- lace Evans, horpe, Middlesbrough, England, assignors to Eri 3: Titan Products Qompan Limited,

England, a British company No Dral Filed Dec. 4, 1957, Ser. No. 70%,555 Claims priority, application Great Britain, July 16, 1952, 17,971/52 23 Qlairns. (Cl. 20 3-61) This application is a continuation-in-part of our copending application Serial No. 366,611, filed July 7, 1953, now forfeited.

This invention relates to the preparation of titanium tetrahalide, particularly titanium tetrachloride.

According to this invention, it has been found that titanium tetrahalides, such as titanium tetrachloride, may be produced by electrolyzing a fused bath which is inert to the desired halogen and has a low solubility (less than 5 grams per liter) for the titanium tetrahalide evolved, using an anode which comprises a titanium compound which reacts with halogen to evolve the titanium tetrahalide. The anode may advantageously be of a mixture of an oxide of titanium (TiO Ti O etc.) with carbon, or of titanium carbide or titanium cyanonitride. Alternatively, the anode may comprise a core of electroconductive material such as carbon, platinum or the like, with the titanium bearing material surrounding the core and adjacent to or in contact therewith.

Where a mixture of titanium oxide and carbon is used, the amount of carbon normally is at least percent by weight and may be as high as 100 percent by weight (or even somewhat higher) of the weight of the titanium oxide.

Where the titanium oxide is pure, only titanium halide is evolved. Where the titanium oxide contains other metals such as iron, vanadium or the like, the halides of these metals are also formed and vaporized. Normally, it is desirable to use materials in which the titanium content is at least 10 to percent by weight of titanium. Rutile and ilmcnite ores as well as titanium slags are suitable materials.

In the practice of the process, an electric current is passed through the fused bath and the titanium tetrahalide is evolved at the anode and is withdrawn from the bath. The fused bath is composed entirely or at least preponderantly of alkali metal halides and/or alkaline earth metal halides in fused state. Such a bath is essentially inert to the halogen of the tetrahalide formed and also is essentially inert to the titanium tetrahalide evolved. Thus, it contains essentially no free alkali. Typical salts which may be used are sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride or the corresponding fluorides, brornides or iodides or mixtures of two or more of the above salts.

As a consequence of the electrolysis, the halogen migrates to the anode and the tetrahalide is formed and vaporized.

Preferably, only one halogen radical is present in the electrolysis bath. The selection of the salts may depend on the temperature at which it is desired to operate and the mixture may be selected to correspond with the eutectic mixture of the salts selected, or, in the case of compound formation, of one or other of the eutectics or even of the intermediate or compound mixtures.

The fused salt electrolysis bath, subsequently referred to as the cell, may be constructed of silica or other ceramic or refractory material heated internally or externally to temperatures of from 700 to 1440' C. (prefer ably between 800 and 1200 C.) by any suitable means. Alternatively, the cell may be constructed of a material which will, at the same time, serve as the cathode. Thus, it may be constructed of tantalum or graphite or other material which will be unattacked by alkali or alkaline earth metal.

The cathode may be liquid consisting of zinc or cadrnium or similar metals. For most purposes, however, a tantalum or carbon, e.g. graphite or iron, cathode is employed.

in the course of the electrolysis, the alkali metal or alkaline earth metal of the halide bath is liberated at the cathode, usually in liquid state. This liberated metal should be restrained from contacting the anode or the titanium tetrahalide evolved from the electrolysis. The anode may be separated from the cathode by means of a diaphragm, such as a porous pot, but, in some cases, a non-porous barrier or darn immersed just below the surface of the fused mass in order to prevent surface layers of liquid metal flowing to the vicinity of the anode, or other means for segregating the products evolved at the cathode from those evolved at the anode, may be provided.

The top of the cell may be sealed with a cover and through this cover electrodes are fixed and supported. Ports may be provided for the removal of gases from the anode and cathode compartments. In some cases it may be necessary to provide a neutral or an inert atmosphere above the electrodes. The atmosphere at the anode may be the halogen itself but generally comprises oxides of carbon and halide vapor generated at the anode. However, other gases may be tolerated at the anode, including nitrogen and the rare gases. The atmosphere above and around the cathode may be nitrogen, helium or argon or other material providing an inert atmosphere. Provision may also be made, if necessary, to evacuate the cell to facilitate the removal of the products of reaction from the cathode and anode compartments, respectively. Alternatively, the cell can be made to operate under pressure.

The titanium compound may be synthetic oxide prepared by any of the well known methods or it may be a natural oxide, such as mineral rutile, mineral brookite or mineral anatase isolated from rock deposits or beach sands, or other material mentioned above. Titanium oxide compound may be admixed in powdered form with powdered carbon, such as charcoal or petroleum coke. T he titanium compound or intimate mixture of oxide or like compound with carbon may be packed into a porous pot with a carbon or other conductive core or anode inserted within the pot. Alternatively, the titanium compound or oxide-carbon mixture, with the aid of a bonding agent such as coal, gum, pitch or glue, may be compressed and a conductive core such as a carbon electrode inserted into the compressed mass. The compound in pulverulent state can be made into a paste of glycerine or dehydrated castor oil, with or without the presence of water, and this paste may be shaped, dried, and baked or fired, preferably in a non-oxidizing atmosphere, with or without a core of carbon, at to 1400" C., to give a hard, electrically conducting mass which will function as the anode.

A further method may consist of packing either the titanium compound or composition to be chlorinated in loose lump form into a porous pot with the carbon anode inserted therein, or, in certain cases, either loosely packed lumps or compressed powder as described above may be inserted into a hollow porous carbon anode from which the titanium tetrahalide subsequently generated may be withdrawn. Carbon dioxide or carbon monoxide may be formed and volatilized when titanium oxide and carbon are used as the chlorinatable composition. Such gases, when generated, are withdrawn, and the titanium tetrahaiide may be condensed away from the carbon gases by well known procedures.

If it is desired to make the process operate continuously, a mixture, preferably finely divided, of the titanium composition with or without a bonding agent may be fed in the form of a thick paste on the top surface of a slowly decaying anode which periodically or continuously will be lowered in the bath as it becomes eaten away. The paste so fed to the anode will dry, cake, and Ulilmately bind and cement together in the form of a hard adherent mass suitable to function as an anode, by heat transmitted through the submerged part of the anode and by heat derived by convection and radiation of the anode chamber.

The titanium tetrahalide gases may be withdrawn from the anode compartment continuously, and preferably they will be condensed and, if necessary, further purified, e.g., by fractional distillation or other well known means, according to the purpose for which they are to be used. The metals formed at the cathode, if in the form of liquid alkali or liquid alkaline earth metal, may be intermittently or continuously discharged. Alternativcly, they may be withdrawn in the gaseous form.

The titanium tetrahalide formed may be used for the production of pigments both by hydrolysis of aqueous solutions of titanium tetrahalide or by vapor phase reactions of titanium tetrahalide, either with steam or by oxidation, to yield pigments of a very high degree of whiteness and of high tinting strength corresponding to the best anatase and rutile pigments available. The titanium tetrahalides may also be used in connection with organic materials to produce a wide variety of organotitanium compounds, e.g., titanium organic amides and titanium organic esters.

Following is a description, by way of example, of methods of carrying the invention into etfect:

Example I A graphite rod was covered with paste consisting of coal and Ti in dehydrated castor oil, and the whole was dried and fired. The resulting electrode and a tantalum rod cathode were inserted in a porous pot inside a cell containing a mixture of sodium chloride and potassium chloride in equal quantities heated to 900 to 1000 C. The melt was electrolyzed with an anode current density of 11 amperes per square decimeter and a cathode current density of 68.8 amperes per square decimeter, and, under these conditions, titanium tetrachloride was formed at the anode.

Example 11 A molten bath was employed containing 50 percent potassium chloride and 50 percent sodium chloride and maintained at 820 C., using an anode prepared by mixing titanium oxide and coal and pre-fired in a nonoxidizing atmosphere, and a cathode consisting of a carbon rod, the anode department being sealed. to permit only the extraction of gases. The cell was operated with an anode current density of amperes per square decimeter and a cathode current density of 62.5 amperes per square decimeter, and, at the anode, titanium tetrachloride was liberated admixed with carbon dioxide and some carbon monoxide, and the titanium tetrachloride was subsequently recovered by condensation.

What is claimed is:

1. A process for producing a volatile titanium tetrahalide which comprises electrolyzing a fused bath of at least one member of the group consisting of alkali metal halides and alkaline earth metal halides, said bath being substantially inert to elemental halogen, with an anode comprising a titanium compound which reacts with halogen to form titanium tetrahalide vapor at a temperature of 700 to 1400 C. while maintaining the temperature of the bath at between 700 to 1400 C., preventing metal evolved at the cathode from contacting the product evolved at the anode and thereby producing the titanium tetrahalide vapor, and removing the vapor from the bath.

2. A process for producing a volatile titanium tetrachloride which comprises electrolyzing a fused bath of at least one member of the group consisting of alkali metal chloride and alkaline earth metal chloride, said bath being substantially inert to elemental chlorine, with an anode comprising a titanium compound which reacts with chlorine to form a volatile chloride at a temperature of 700 to 1400 C. while maintaining the temperature of the bath at between 700 to 1400" C. and thereby producing titanium tetrachloride vapor, and removing the evolved tetrachloride from the bath while preventing metal evolved at the cathode from contacting the evolved titanium tetrachloride.

3. The process of claim 1 wherein the anode comprises a mixture of carbon and titanium dioxide in which the carbon concentration is at least 10 percent by weight based upon the titanium dioxide.

4. The process of claim 2 wherein the titanium compound is titanium oxide mixed with at least 10 percent by weight of carbon based upon the weight of the titanium oxide.

5. The process of claim 1 wherein the anode is a member of the group consisting of titanium dioxide and carbon, titanium carbide, and titanium cyanonitride.

6. The process or" claim 2 wherein the anode is a member of the group consisting of titanium dioxide and carbon, titanium carbide, and titanium cyanonitride.

'7. A method of preparing titanium tetrahalide which comprises electrolyzing a fused bath consisting of a member of the group consisting of alkali metal halides and alkaline earth metal halides in which the halide component is that of the halide of the titanium compound desired with an anode comprising a mixture of carbon with a material containing at least percent of TiO the amount of carbon being at least stoichiometrically equivalent to the amount of Ti0 present in said material, maintaining the temperature of the bath 700 to 1400 C., maintaining a neutral atmosphere over the electrodes whereby titanium tetrahalide is formed, and vaporizing and removing the titanium tetrahalide from the bath.

8. The process of claim 7 wherein the titanium tetrahalide is titanium tetrachloride, and the halides are chlorides.

9. The process of claim 2 wherein the compound is titanium carbide.

10. The process of claim 2 wherein the compound is titanium cyanonitride.

11. The method of producing TiCl in an electrolytic cell which comprises electrolyzing a fused NaCl bath wherein the anode of the electrolytic cell is composed of a T iC containing material submerged in said fused bath, separating the volatilized TiCl at the anode compartment and recovering the pure Na metal at the cathode compartment.

12. A method of producing a titanium halide of the group consisting of the chloride, bromides, and iodides, which comprises electrolyzing a fused bath of salts of the group consisting of alkali halides, alkaline earth halides, and mixtures thereof, the halides comprising the group consisting of chlorides, bromides, and iodides, using as the anode material a titanium carbide containing material, separating the volatilized titanium halide at the anode compartment, and recovering metal of the halide of said group at the cathode.

13. A method of producing a titanium halide of the group consisting of the chlorides, bromides, and iodides, which comprises electrolyzing a fused bath of salts of the group consisting of alkali halides, alkaline earth halides, and mixtures thereof, the halides comprising the group consisting of chlorides, bromides, and iodides, using as the anode material a titanium compound which reacts with 5 halogen to form titanium tetrahalide vapor at a temperature of 700 to 1400 C., separating the volatilized titanium halide at the anode compartment, and recovering metal of the halide of the bath at the cathode.

14. In the method of producing titanium tetrahalides of 5 the group consisting of chlorides, bromides and iodides, the steps of electrolyzing a fused bath of separated anode and cathode compartments of the salts of the group consisting of the alkali halides, alkaline earth halides, and mixtures thereof, said halides comprising the group consisting of chlorides, bromides, and iodides, using as the anode electrode compacted pulverized titanium carbide containing material, said anode electrode being at least partially submerged in said fused salt bath thereby causing gaseous titanium tetrahalides to form at the anode and at the same time the pure metal of said halides at the cathode, and collecting and condensing the vapors of said titanium tetrahalides from the upper portion of said anode compartment.

15. The method of claim 14 wherein the halide is a chloride.

16. The method of claim 14 wherein the fused bath consists of NaCl.

17. The method of claim 14 wherein the fused bath consists of Mgcl 18. The method of claim 14 wherein the halide is an iodide.

19. The method of claim 14 wherein the fused bath consists of NaI.

20. The method of claim 14 wherein the fused bath consists of an eutectic mixture of LiCl and KCl.

21. The method of claim 14 wherein the fused bath consists of an eutectic mixture of NaCl and CaCl 22. The method of claim 14 wherein the fused bath consists of an eutectic mixture of NaCl, KCl, and Mgcl 23. The method of claim 14 wherein the fused bath is maintained at temperatures between 700900 C.

References Cited by the Examiner UNITED STATES PATENTS 568,231 9/95 Blackman 204-61 2,734,855 2/56 Buck et a1. 204-61 2,870,071 1/59 Juda et al 204-61 FOREIGN PATENTS 635,267 4/50 Great Britain.

744,396 2/56 Great Britain.

265,899 3/50 Switzerland.

WINSTON A. DOUGLAS, Primary Examiner.

JOHN R. SPECK, JOSEPH REBOLD, Examiners. 

1. A PROCESS FOR PRODUCING A VOLATILE TITANIUM TETRAHALIDE WHICH COMPRISES ELECTROLYZING A FUSED BATH OF AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF ALKALI METAL HALIDES AND ALKALINE EARTH METAL HALIDES, SAID BATH BEING SUBSTANTIALLY INERT TO ELEMENTAL HALOGEN, WITH AN ANODE COMPRISING A TITANIUM COMPOUND WHICH REACTS WITH HALOGEN TO FORM TITANIUM TETRAHALIDE VAPOR AT A TEMPERATURE OF 700 TO 1400*C. WHILE MAINTAINING THE TEMPERATURE OF THE BATH AT BETWEEN 700 TO 1400*C., PREVENTING METAL EVOLVED AT THE CATHODE FROM CONTACTING THE PRODUCT EVOLVED AT THE ANODE AND THEREBY PRODUCING THE TITANIUM TETRAHALIDE VAPOR, AND REMOVING THE VAPOR FROM THE BATH. 